1. Field of the Invention
The present invention relates to an information processing apparatus and a power supply control method. More particularly, it relates to an information processing apparatus and a power supply control method in which provisions are made to reduce the time required to resume from a power-saving mode.
2. Description of the Related Art
In recent years, with improvements in CPU performance, coupled with increased hard disk capacity, PC/TV combinations which allow users to enjoy television programs and video recordings on personal computers (PCs) have been finding widespread use in homes. As PC/TV combinations have become widespread, the slow startup time of PCs, compared to the startup time of TVs, has become important. To improve the startup time of PCs and achieve power saving at the same time, power management standards (such as ACPI: Advanced Configuration and Power Interface) have been defined. ACPI S3 defines a “standby” mode, that is, a “suspend-to-RAM” mode. In standby mode when power is turned off, graphics functions and devices including hard disks are shut down, but power is supplied to the memory so that any work data is preserved. As the work data is preserved in the memory, it takes only a few seconds to resume from standby mode. Further, work can be resumed where it was left off.
ACPI S4 defines a “hibernation” mode, that is, a “suspend-to-disk” mode. In hibernation mode, after saving memory contents to a hard disk, all devices including the memory are shut down. When power is turned on again, the contents saved on the hard disk are written into the memory to resume. Hibernation mode can save more power than standby mode, but when the resume speed is compared, between hibernation and standby, it is much quicker to resume from the standby state in which the memory contents are preserved.
Here, when a comparison is made between resumption from standby mode and resumption from hibernation mode, the execution of the BIOS (Basic Input/Output System) takes about 0.5 second after power on from standby mode and 7 to 10 seconds from hibernation. After that, it takes 2 to 5 seconds to load the OS (Operating System) in the case of standby mode and 13 to 20 seconds in the case of hibernation mode. That is, it takes about 5 seconds to complete the loading of the OS after power on from standby mode and about 20 to 30 seconds after power on from hibernation. ACPI S5 defines a normal power-off mode, and it takes much longer to resume, that is, about 60 seconds, because a reboot is needed.
A personal computer equipped with a television function is usually used by connecting it to a commercial power line in a home; accordingly, unlike notebook computers, there is no concern of losing memory contents due to battery exhaustion. It is therefore desirable that the computer be placed in standby mode when shutting it off, if it is desired to quickly restart when power is turned on next. However, the problem is that, if the power supply is cut off during standby mode because of the disconnection of the AC plug or the occurrence of a power outage, the data stored in the memory will be lost. In particular, when the personal computer is used in the same way as a television set in a home, there are cases where the AC plug is disconnected upon power off for the purpose of power saving. If this happens when the computer is in a standby state, the work data saved in the memory will be lost.
A similar situation can happen in the case of a battery-operated personal computer; that is, if the battery runs down during standby mode, the data saved in the memory will be lost. Therefore, when safety is considered, using only the standby mode for power saving involves a problem. On the other hand, hibernation mode has the problem of slower startup time.
Traditionally, it has been known that a notebook computer or the like equipped with a resume function to resume from hibernation mode has the problem that it takes time to resume from hibernation mode. To solve this problem, there has been proposed a computer system in which when AC power supply is available, memory contents are saved on a hard disk upon turning off of the power switch, but power is continued to be supplied to the memory and, when the power switch is turned on next, the system is restored to the operating state from the hibernation state (Japanese Unexamined Patent Publication No. 10-97353). In the proposed system, a standby function is incorporated in a personal computer having the function of resuming from hibernation, and the system quickly resumes from standby mode when the power supply is on, but resumes from hibernation mode when the power supply is interrupted.